Electroactive actuators are solid state devices which produce movement or change in dimensions when an electric potential or voltage is applied to them. These devices are constructed with multiple stacked layers of metalized dielectric material having piezoelectric or electrostatic properties.
Electroactive actuators typically require operating voltage ranging from 50 volts D.C. to 500 volts D.C., since their sensitivity of movement to applied voltages are relatively low. Since this operating level of voltage is normally not found in many applications, a D.C. to D.C. converter is commonly used to convert available voltage to the proper operating voltage required by the actuator. Frequently this operating voltage must be changed upon command, in order to produce variations in movement.
The present invention permits integration of the low voltage to high voltage D.C. to D.C. converter with the actuator. This integration results in the converter being compact in size and achieves simplicity of design.
Achieving small physical size in a power supply or D.C. to D.C. converter applications is presently commonly realized by using relatively high switching frequencies for power conversion. However, there is considerable practical difficulty in producing relatively high voltage outputs (in the range of 100 to 500 volts D.C.) from low voltage sources (in the range of 5 to 28 volts D.C.) with small physical size.
The problem in the aforesaid designs is that large step up turn ratios are required in the power supply transformer. For example, in constructing a power supply with a 5 volt D.C. input and a 300 volt D.C. output, a transformer turns ratio of approximately 60:1 would normally be required.
However, a large transformer with a high turns ratio would have large parasitic component inductances and capacitances. Such a transformer would be far from an ideal transformer. A large portion of the input power goes into energy stored in these parasitic components. When driven with a rectangular waveform, such a transformer tends to produce a rounded, or sinusoidal output. Although it is possible to work around these resonant effects, the results is that the transformer is physically larger than would be otherwise, since it is also storing considerable energy in the parasitic inductances and capacitances.
In the topology described hereinafter, and depicted in the present invention, the aforedescribed effect of poor coupling is mitigated, allowing the compact construction of electroactive actuators.
Furthermore, in the present invention, the electroactive actuator itself is used as an integral circuit element. This permits additional miniaturization. Instead of using a discrete capacitor, the electroactive actuator is tapped or segmented, and used as a filter capacitor. Conventional connections to the interior layers of the actuator permit such usage.